The allenyl .beta.-lactam compound of the invention represented by the formula (II) is conventionally prepared, for example, by reacting a tertiary organic base with the starting material in an organic solvent according to the process disclosed in JP-A-282359/1992. However, this compound as contained in the resulting reaction mixture is unstable owing to the presence of an excess of the tertiary organic base or a salt of the base and sulfonic acid, so that the reaction mixture usually requires repetition of a cumbersome procedure involving extraction and concentration after the completion of the reaction. This procedure takes time in the case of quantity production, consequently entailing problems such as a marked reduction in the yield of the isolated product. Thus, a satisfactory feasible process has yet to be developed for preparing the allenyl .beta.-lactam compound.
Reports have been made on widely acceptable processes for preparing 3-halogenated cephem derivatives represented by the formula (III). These processes include a process which uses a 3- hydroxycephem compound represented by the formula (IV) and serving as the starting material and involves conversion of the hydroxyl group to trifluoromesyloxy group and the subsequent reaction with a lithium halide as disclosed in J. Org. Chem., 54, 4962(1989), a process wherein a reactive chlorine or bromine compound (such as phosphorus trichloride, phosphorus oxychloride or thionyl bromide) is reacted with a 3-hydroxycephem compound in dimethylformamide as disclosed in JP-A- 116095/1974, and further a process wherein an alkali metal salt or alkaline earth metal salt of a halogen is reacted with an allenyl .beta.-lactam compound as disclosed in JP-A-282387/1992 ##STR4## wherein R.sub.1 and R.sub.3 are as defined below.
The first of the processes requires the use of the 3-hydroxycephem compound as the starting material which compound itself is difficult to prepared and is therefore in no way practically feasible. The second process inevitably forms 3-sulfonylcephem or 3-thiocephem as a by-product due to the recombination of sulfinate ion or thiolate ion which is released on ring closure, consequently giving the desired 3-halogenated cephem derivative in a yield of as low as up to 70%.
An object of the present invention is to overcome the drawbacks of the foregoing conventional processes and to provide a process capable of readily preparing the desired allenyl .beta.-lactam compound and 3-halogenated cephem compound from the same starting material in a high yield with a high purity merely by using different reaction conditions for the different compounds.